The food industry is concerned with how quickly most fruits (and various fruit products) become discolored upon exposure to air. The discoloration upon exposure to air is caused by a chemical reaction known as oxidation. Oxidation (typically indicated by discoloration) of fruits involves an enzyme-catalyzed oxidation of phenolic compounds present in the fruit. Browning of fruits is also a concern of the food industry. Browning of a fruits typically occurs following a mechanical injury to the fruit, such as during the harvesting or processing of such foods.
Bisulfite compounds are currently used to inhibit the enzymatic oxidation and browning in "fresh-cut" and processed fruits. Since a segment of the population is hypersensitive to sulfites, however, food processors prefer to avoid using sulfite compounds. Further, concern over labeling requirements for sulfur dioxide (due to allergic reactions by many users) also causes food processors to avoid its usage. It is particularly desirable in the food industry that an oxidation/browning inhibitor composition be derived from a natural source, rather than a synthetic chemical. That is, main-line food processing companies are seeking effective, natural alternatives to synthetic food additives. Additionally, the FDA typically requires less extensive testing information for a preparation derived from a natural source than for a preparation derived from a synthetic chemical. This is particularly true if the "natural source" is a common foodstuff.
Other currently available oxidation and browning inhibitors include, for example, 4-hexyl resorcinol, sulfurdioxide metal chelators such as citric acid and phosphates in combination with ascorbic acid. Oxidation and browning inhibitors such as citric acid and phosphates in combination with ascorbic acid, however, are not sufficiently effective. The use of inhibitor 4-hexyl resorcinol is limited in the United States to use with shrimp. Additionally, even if 4-hexyl resorcinol is approved for use with fruits and fruit products, many food processors will likely be reluctant to use it because it is derived from a synthetic chemical rather than from a natural source.
Pineapple juice has also been shown to inhibit browning and oxidation of fresh fruit (P. G. Lozano-de-Gonzalez, D. M. Barrett, R. E. Wrolstad, and R. W. Durst, Enzymatic Browning Inhibited in Fresh and Dried Apple Rings by Pineapple Juice, J. Food Sci. Vol. 58, pp. 399-404 (1993)). The antibrowning/antioxidant effectiveness of pineapple juice is, however, unacceptably variable for use in the food industry. That is, the effectiveness of pineapple juice for such purposes varies from one type of pineapple to another, and from one pineapple to another within a particular pineapple type. The effectiveness of the pineapple juice as an antibrowning/antioxidizing agent also varies depending upon where the pineapple was grown.
The present invention provides natural-source compositions having effective and consistent antibrowning and antioxidant characteristics. Additionally, the present invention provides methods for making the antibrowning/antioxidant compositions of the present invention. More specifically, the present invention provides natural browning and oxidizing inhibitor compositions comprising S-sinapyl-L-cysteine, N-L-.gamma.-glutamyl-S-sinapyl-L-cysteine, S-sinapyl glutathione, or various mixtures thereof.
Methods for making such natural, antibrowning/antioxidant compositions from pineapple juice and/or from pineapple processing plant waste streams are also provided. The present invention provides methods for making antibrowning/antioxidant compositions that are efficiently and effectively separated from sugars, acids, and other phenolic compounds present in pineapple juice and/or pineapple processing plant waste streams.
More specifically, one method of the invention generally includes centrifuging and filtering a quantity of pineapple juice to obtain a filtrate. The filtrate is applied to a resin column. The resin column is washed with acidified water to remove undesirable constituents, such as sugars, acids, and other polar compounds. The constituents of the antibrowning/antioxidant compositions are eluted from the column using a suitable media such as an alcohol. The eluate constituents are evaporated to dryness and re-dissolved in a liquid, such as water. The re-dissolved constituents are applied to an anion-exchange resin column. The anion-exchange resin column is washed to remove undesirable, neutral phenolic compounds. The anion-exchange resin column is then treated with an acidic liquid, such as sulfuric acid. The acidic liquid elutes the remaining constituents from the column to produce an eluate. The eluate is neutralized to form one of the present invention antibrowning/antioxidant compositions. One or more of the individual constituents of the neutralized eluate may be isolated to make alternative embodiments of the antibrowning/antioxidant compositions of the present invention.
The foregoing and other features and advantages of the present invention will become more apparent from the following detailed description, drawings, and examples of the browning, oxidation inhibiting compositions and methods for preparing the same.